It is known in the art that there are problems associated with protecting the occupant of a vehicle seat in the event of the vehicle being involved in a side impact. If a vehicle is involved in a head-on impact, then there are typically relatively large regions of the vehicle that may crumple and deform to absorb some of the energy associated with the impact, for instance the bonnet and engine of the vehicle. In addition, occupants of front seats of a motor vehicle tend to be seated at least around arm's length from the dashboard in front of them, and so there is a relatively large space in which to inflate an air-bag to cushion the impact experienced by passengers.
Further, the time between the beginning of the impact (i.e. the front bumper of the vehicle contacting another object) and large acceleration forces acting on vehicle occupants is relatively long, largely as a result of the presence of considerable forward crumple zones, as discussed above.
Vehicle occupants are generally less well-protected in the event of a side impact, however, as the thickness of the vehicle exterior wall is typically much less than the thickness of the front portions of the vehicle. In addition, the occupant is usually positioned relatively close to the vehicle's side wall. This means that very little crumple zone is available, and relatively little deformation of the side of the vehicle is required before the side of the vehicle comes into direct contact with the occupant. Further, the length of time between the start of the impact and large acceleration forces acting on the seat occupant is small.
One approach to reducing injuries in the event of a side impact is disclosed in US2009/0020988, which discloses a vehicle seat having two air-bags mounted on an exterior side thereof (i.e. the side closest to the exterior wall of the vehicle on the side of the vehicle on which the seat is installed). One air-bag is a conventional side impact air-bag, which inflates to occupy a position between the vehicle's exterior side wall and the seat occupant. The second air-bag inflates, remaining within an outboard part of the seat, causing the outboard part of the seat to expand and swell, thus pushing the occupant of the seat both forward and inwardly towards the centre of the vehicle. The second air-bag is activated at as early a stage as possible in a crash situation, with the aim being to increase the distance between the seat occupant and the vehicle's side wall.